1. Field of the Invention
The present invention relates to a noise reduction apparatus which reduces noise in an image signal.
2. Description of the Related Art
Noise reduction apparatuses for image signals can be found in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-157057 and Jpn. Pat. Appln. KOKAI Publication No. 2002-247412. Jpn. Pat. Appln. KOKAI Publication No. 2001-157057 discloses an apparatus wherein a noise amount is converted into a function with respect to a signal level, and the frequency characteristic of filtering is controlled in accordance with the noise amount estimated on the basis of this function, thereby performing noise reduction processing adaptive to the signal level. Further, Jpn. Pat. Appln. KOKAI Publication No. 2002-247412 discloses an apparatus wherein a focused pixel is classified into an original image signal component (hereinafter referred to as an original signal), a noise component and an uncertain component on the basis of signal values of the focused pixel and neighboring pixels thereof, and different kinds of processing are performed for the respective components, thereby reducing noise while restraining deterioration of the original signal.